1. Field of the Invention
The present invention relates to a scroll compressor suited for use in, for example, an air conditioner, a refrigerator or the like.
2. Description of Related Art
The scroll compressor and its operating principle are disclosed in numerous patent and technical literature and are, therefore, well known to those skilled in the art. As an example of the scroll compressor, U.S. Pat. No. 4,492,543 (corresponding to Japanese Patent Publication No. 61-15276) or U.S. Pat. No. 4,411,604 (corresponding to Japanese Patent Publication No. 58-55359) discloses an open scroll compressor for use in an automotive air conditioner, as shown in FIGS. 8 and 9. The scroll compressor disclosed in U.S. Pat. No. 4,492,543 employs a ball joint assembly which serves both as a thrust support for supporting a thrust force applied to an orbiting end plate of an orbiting scroll member and a rotation constraint element for preventing rotation of the orbiting scroll member about its own axis while permitting it to undergo an orbiting motion relative to a stationary scroll member. On the other hand, the scroll compressor disclosed in U.S. Pat. No. 4,411,604 includes a compressor housing made up of a cup-like casing and a front end plate secured to each other. In FIGS. 8 and 9, the construction for transmitting a drive force from an engine to a compressor body through a belt and an electromagnetic clutch is omitted, because it is well known to those skilled in the art.
The scroll compressor shown in FIGS. 8 and 9 comprises a generally cylindrical compressor housing 3 made up of a cup-like casing 37 and a front end plate 38 with an open end of the cup-like casing 37 closed by the front end plate 38. A stationary scroll member 1, including a stationary end plate 1a and a stationary scroll wrap 1b protruding axially from one end surface of the stationary end plate 1a, and an orbiting scroll member 2 similarly including an orbiting end plate 2a and an orbiting scroll wrap 2b protruding axially from one end surface of the orbiting end plate 2a are operatively accommodated within the compressor housing 3 with the stationary and orbiting scroll wraps 1b and 2b engaging with each other to define a plurality of volume-variable, sealed working pockets 10 therebetween. A ring-shaped first race 71, a first ring 72, a plurality of ball elements 76, a second ring 74, and a ring-shaped second race 73, all of which serve both as thrust support elements and rotation constraint elements, are disposed in this order between the orbiting end plate 2a and the front end plate 38. All of the ring-shaped first race 71, first ring 72, second ring 74, and ring-shaped second race 73 have a generally flat configuration and extend in parallel to the orbiting end plate 2a. A drive mechanism for imparting an orbiting motion to the orbiting scroll member 2 is disposed between the ring-shaped second race 73 and the front end plate 38. The stationary scroll member 1 has a plurality of fastening legs 1d formed on the rear surface of the stationary end plate 1a with the fastening legs 1d fastened to the cup-like casing 37 by means of bolts 19. The stationary end plate 1a of the stationary scroll member 1 has a seal groove 1f defined therein along a peripheral portion 1e thereof, in which an O-ring 18 is received to seal between a high-pressure chamber 11 and a low-pressure chamber 12 both defined within the compressor housing 3 and partitioned by the stationary end plate 1a. The first ring 72 is mounted on the orbiting end plate 2a so as to cover the ring-shaped first race 71, while the second ring 74 is mounted on the front end plate 38 so as to cover the ring-shaped second race 73 with a relatively narrow gap defined between the first and second rings 72 and 74. Each of the first and second rings 72 and 74 has a plurality of regularly spaced holes 75 of an identical size defined therein, and the holes 75 in the first ring 72 are axially aligned with those 75 in the second ring 74. The plurality of ball elements 76 referred to above are interposed between the first and second rings 72 and 74, and are received in both the holes 75 of the first ring 72 and those 75 of the second ring 74, thereby preventing rotation of the orbiting scroll member 2 about its own axis while permitting it to undergo an orbiting motion relative the stationary scroll member 1. A drive shaft 9 is rotatably supported by a main bearing 15 securely mounted in the compressor housing 3 and has a main shaft portion 9a extending through a sealing assembly 17 and an auxiliary bearing 16 so as to protrude outwardly from the compressor housing 3. The drive shaft 9 has a rear end integrally formed with an eccentric drive pin 9b having its longitudinal axis parallel to, but offset a predetermined distance laterally from the longitudinal axis of the drive shaft 9. The eccentric drive pin 9b is received in an orbiting bush 8 employed as one of the drive mechanism. The orbiting bush 8 is inserted into an orbiting bearing 7, which is in turn inserted rotatably into a cylindrical boss 2c integral with the orbiting end plate 2a of the orbiting scroll member 2, to thereby complete an orbiting mechanism required for orbiting the orbiting scroll member 2 relative to the stationary scroll member 1. The cup-like casing 37 has a suction port 13 defined therein on the side of the low-pressure chamber 12 to introduce refrigerant employed as a working fluid therein and, also, has a discharge port 14 defined therein on the side of the high-pressure chamber 11 to discharge the refrigerant therefrom.
When a compression stroke is started by the orbiting motion of the orbiting scroll member 2 relative to the stationary scroll member 1, the refrigerant is drawn into the low-pressure chamber 12 through the suction port 13. The refrigerant is then introduced into the sealed working pockets 10 delimited by the stationary end plate 1a, stationary scroll wrap 1b, orbiting end plate 2a, and orbiting scroll wrap 2b, and is compressed as it moves from peripheral portions of the stationary and orbiting scroll wraps 1b and 2b towards a central portion. The compressed refrigerant is subsequently discharged into the high-pressure chamber 11 through a center discharge hole 1c defined in the stationary end plate 1a and flows out from the compressor housing 3 through the discharge port 14.
Japanese Laid-open Patent Publication (unexamined) No. 4-116201 discloses a method of assembling a scroll compressor as shown in, for example, FIGS. 8 and 9. According to this disclosure, when the open end of the cup-like casing 37 is closed by the front end plate 38, one or more shims 20 are sandwiched between mating surfaces of the cup-like casing 37 and the front end plate 38 to regulate an axial gap between the stationary and orbiting end plates 1a and 2a, thereby maintaining predetermined axial gaps between axial end surfaces of the stationary and orbiting scroll wraps 1b and 2b and associated orbiting and stationary end plates 2a and 1a opposed thereto.
Japanese Laid-open Utility Model Publication (unexamined) No. 4-87380 discloses a scroll compressor shown in FIG. 10 and comprising a stationary scroll member 1, an orbiting scroll member 2, an orbiting mechanism, a drive shaft 9, and a drive mechanism, all of which are generally identical in construction to those of the scroll compressor shown in FIGS. 8 and 9. Although a compressor housing 3 shown in FIG. 10 is made up of a cup-like casing 37 and a front end plate 38, like the compressor housing shown in FIGS. 8 and 9, the front end plate 38 is a two-component member made up of an annular front plate 38a and a cylindrical member 38b rigidly secured to each other, unlike the compressor housing shown in FIGS. 8 and 9. The compressor housing 3 shown in FIG. 10 accommodates a thrust support element in the form of a generally flat thrust bearing 4 and a rotation constraint element in the form of an Oldham ring 5 both interposed between the orbiting end plate 2a and the annular front plate 38a.
In this construction, the axial gaps between the scroll wraps 1b and 2b and the associated end plates 2a and 1a opposed thereto can be regulated by appropriately changing the thickness of the thrust bearing 4, instead of changing that of the shims.
FIG. 11 depicts a method of assembling the scroll compressor. As shown therein, the front end plate 38 is first placed on a mount 48 with its open end directed upwardly and is subsequently coupled with the drive mechanism and the orbiting mechanism. The orbiting scroll member 2 is then incorporated into the front end plate 38 with the orbiting scroll wrap 2b directed upwardly. At this moment, the distance A2 between the upper surface of the orbiting end plate 2a and the mating surface of the front end plate 38 with the cup-like casing 37 is measured using a measuring instrument 50. Likewise, the distance A1 between the lower end surface of the stationary scroll wrap 1b and the mating surface of the cup-like casing 37 with the front end plate 38 is measured using the measuring instrument 50. Then, the cup-like casing 37 is rigidly secured to the front end plate 38 while the axial gaps are being regulated by changing the thickness of the shims 20 or the thrust bearing 4 so that the difference between the two distances A1 and A2 may fall within a permissible tolerance.
The conventional scroll compressors referred to above encounter several disadvantages. By way of example, the ball joint assembly shown in FIGS. 8 and 9 which serves both as a thrust support and a rotation constraint element often causes irregular rolling of the ball elements 76, which in turn generates a relatively large noise. Also, because the thrust force of the orbiting scroll member 2 is supported by the ball elements 76 and the two races 71 and 73 sandwiching the ball elements 76 therebetween, the material thereof is required to be hard and high in rigidity, resulting in an increase in weight. Furthermore, as the speed of the orbiting motion of the orbiting scroll member 2 relative to the stationary scroll member 1 increases, the centrifugal force increases and, hence, each of the main bearing 15 and the orbiting bearing 7 tends to receive an excessively large load. In addition, because the axial gaps vary considerably and are difficult to make constant, the performance and reliability of the compressor is adversely affected thereby. An attempt to reduce the axial gaps or to make them substantially constant results in at least an increase of the kind of shims interposed between the cup-like casing 37 and the front end plate 38. Also, because many element parts including the ball elements 76 and their associated elements are required, it is difficult to maintain the accuracy of such element parts or to accurately assemble the compressor due to irregular rolling of the ball elements, thus hindering an automated assemblage of the compressor.
On the other hand, the conventional scroll compressor shown in FIG. 10 employs a generally flat thrust bearing 4 as a thrust support element and an Oldham ring 5 as a rotation constraint element. Although this construction lowers the noise level compared with the ball joint assembly referred to above, sliding portions of the thrust bearing 4 and those of the Oldham ring 5 are accompanied with sliding friction, and an increase in friction loss results in a decrease in performance. Also, the regulation of the axial gaps between the scroll wraps 1b and 2b and the associated end plates 2a and 1a by an appropriate selection of the thickness of the thrust bearing 4 inevitably increases the kind of thrust bearings. In this case, if an inappropriate thrust bearing is erroneously incorporated into the compressor housing, many element parts including the orbiting scroll member and the like already assembled must be disassembled and then reassembled, taking much time and labor. Moreover, the separated structure of the front end plate 38 results in an increase in manufacturing cost.
Each of the compressor housing 3 shown in FIGS. 8 and 9 and that shown in FIG. 10 is made up of at least two separated members i.e., the cup-like casing 37 and the front end plate 38 with both the suction port 13 and the discharge port 14 defined in the cup-like casing 37. In such a compressor housing 3, the mating surfaces of the cup-like casing 37 and the front end plate 38 are positioned frontwardly (right-hand side in FIG. 8 and left-hand side in FIG. 10) of the front surface of the orbiting end plate 2a and radially outwardly of the drive shaft 9, while the O-ring 18 received in the seal groove 1f of the stationary end plate 1a for sealing between the high-pressure chamber 11 and the low-pressure chamber 12 is positioned deep within the cup-like casing 37. Because of this, if the O-ring 18 is incompletely received in the seal groove 1f during assemblage, the erroneous mounting of the O-ring 18 cannot be readily noticed. Although this results in a gas leakage from the high-pressure chamber 11 to the low-pressure chamber 12 and, hence, can be discovered during a leakage inspection, it is necessary to remove and again incorporate the stationary scroll member 1 from and into the cup-like casing 37. At this moment, whether threaded portions for fastening the stationary scroll member 1 to the cup-like casing 37 have been damaged or not must be checked and leakage from the threaded portions must be checked, requiring much time and labor.
Furthermore, as discussed above with reference to FIG. 11, in order to obtain the predetermined axial gaps referred to above, measurement of the distance between the open end surface of the cup-like casing 37 and the axial end surface of the stationary scroll wrap 1b, and that of the distance between the wrap-side end surface of the orbiting end plate 2a and the mating surface of the front end plate 38 with the cup-like casing 37 must be carried out by moving the measuring instrument 50. Because the stroke (A1 or A2 in FIG. 11) of movement of the measuring instrument 50 is relatively large, the problem arose in that the measurement error tends to become large due to an undesired inclination of the element parts assembled or that of the measuring instrument 50.